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The invention relates generally to management of multiple volumes of data distributed throughout a data storage environment, and more particularly to a system and method for management of device labels used by host systems that interact with data storage systems, when such labels are written as data and distributed over more than one device.
As is known in the art, computer systems generally include a central processing unit (CPU), a memory subsystem, and a data storage subsystem. According to a network or enterprise model of the computer system, the data storage system associated with or in addition to a local computer system, may include a large number of independent storage devices, typically disks housed in a single enclosure or cabinet. This array of storage devices is typically connected to several computers or host processors over a network or via dedicated cabling. Such a model allows for the centralization of data that is available to many users but creates a critical hub for operations.
Recently, disk redundancy has evolved as an alternative or complement to historical backups of the information stored on this critical hub. Generally speaking, in a redundant system, two storage devices, such as disk storage devices, data is copied and stored in more than one place. This allows the data to be recovered if one storage device becomes disabled. In a basic approach, a first disk storage device stores the data and a second disk storage device stores a point-in-time copy of that data. Whenever a data transfer is made to the first disk storage device, the data is also transferred to the second disk storage device. Typically, separate controllers and paths interconnect the two disk storage devices to the remainder of the computer system.
While mirroring has important advantages, it may lead to problems in certain circumstances when all of data including some that is unique to the physical storage device itself is replicated. In particular some host computers use a proprietary operating system that internally manages data storage devices by using xe2x80x9clabels,xe2x80x9d which are typically host-written character strings or some other technique to internally identify disks. For example hosts operating under the Microsoft Windows NT operating system does not allow duplicate labels. This creates problems when data is replicated from one device to another and the labels are replicated as well. When the label is so replicated to at least one other device, the host can encounter two devices carrying the same identification information and treat that as an error.
What is needed is a way to prevent such errors occurring at a host interacting with a data storage system in which data is distributed over one or more disks but while still allowing mirror copying of data to occur.
The present invention is a system and method for management of device identification that is treated as device data, when such data is replicated from one storage device to at least one other storage device.
In one aspect of the invention, the data storage system is configured with logic that enables a method of changing a host-written label, denoted as xe2x80x9cre-labelingxe2x80x9d for a logical volume. Such a logical volume in a preferred embodiment may be one created for continuing business operations while other activities occur that use a copy of the data on the logical volume, wherein such logical volumes may be denoted as a xe2x80x9cbusiness continuance volume (BCV).xe2x80x9d
Re-labeling changes the label originally written by the host on one device and replicated to another device, which received a point-in-time copy of the first device""s data. The re-labeling takes place during a certain operation that takes the BCV offline to a host computer in communication with the data storage system. In the preferred embodiment, the operation that takes the BCV offline is referred to as a xe2x80x9csplit with re-labelxe2x80x9d operation. This re-labeling avoids labeling errors that could arise when duplicate labels result from at least one of the following situations: (i) following a split operation, wherein the BCV has a copy, i.e., an exact replica, of the data from a standard device which has been copied to the BCV; including the identifying label, or (ii) following an operation to xe2x80x9crestorexe2x80x9d the standard device from a device (such as a BCV) having a copy of data originally copied from the standard device. This invention is also useful when a single host encounters two volumes, each distributed, respectively, over a local and remote system.